1. Field of the Invention
The present invention relates to an optical member, a light source device, and a display device, and more particularly, to an optical member included in a liquid crystal display device or a light source device for a liquid crystal display device which adjusts characteristics of light emitted by a light source, a light source device including the optical member, and a display device.
2. Description of the Related Art
A display device including a non-self-emissive display panel such as a transparent or translucent liquid crystal display panel is generally configured to include light sources on the back side of the display panel or to include a light source device including light sources (also referred to as “a back light device” and “a back light unit”, for example). By illuminating the back side of the display panel with light emitted by the light sources and transmitting the light to the front side, such a display unit can make images visible on the front side of the display panel.
FIG. 15 is an exploded perspective view schematically showing the structure of relevant components of a conventional liquid crystal display device including light sources. A liquid crystal display device 9 shown in FIG. 15 includes a plurality of light sources 91, a liquid crystal display panel 93 (e.g., a transparent liquid crystal display panel), optical members 92 provided therebetween (also referred to as “optical sheets”), and other given members. The characteristics of light emitted by the light sources 91 are adjusted by the optical members 92, and the light illuminates the back side of the liquid crystal display panel 93.
In order to display images with high quality using the liquid crystal display device 9 having the above configuration, the distribution on the surface of the liquid crystal display 93 of the strength of the light illuminating the back side of the liquid crystal display panel 93 needs to be uniform. Thus, the liquid crystal display device 9 is generally configured such that the plurality of light sources 91 are arranged at substantially even intervals, and optical members (e.g., a diffusion plate and a diffusion sheet) capable of diffusing light are provided between the light sources 91 and the liquid crystal display panel 93 as shown in FIG. 15.
With the upsizing of liquid crystal display panels, the total amount of the light illuminating the back side of the liquid crystal display panel having the above configuration needs to be increased according to the screen size. Generally, the amount of light is increased by increasing the number of light sources included in a light source device or a display device.
However, increasing the number of light sources included in the light source device or the display device increases the number of components of the light source device or the display device, which results in an increased cost of components. If fluorescent tubes are used as light sources, the number of the fluorescent tubes needs to be increased, and the number of components such as inverters for driving the florescent tubes also needs to be increased. In addition, the increased number of light sources means an increased total amount of electricity for driving the light sources, which results in an increased power consumption of the light source device or the display device. This runs counter to the trend of power saving.
To solve the above problems, a configuration may be used in which the intervals between adjacent light sources (i.e., arrangement intervals between light sources) are made narrower in the area corresponding to the center portion of the screen of the liquid crystal display panel and are made wider in the areas corresponding to the end portions of the screen (see Japanese Patent Application Unexamined Publication No. Hei06-75216, Japanese Patent Application Unexamined Publication No. 2002-82626, and Japanese Patent Application Unexamined Publication No. 2005-347062). This configuration makes it possible to reduce the number of the light sources in the areas corresponding to the end portions of the screen compared to the configuration of arranging the light sources at even intervals. Accordingly, it is possible to reduce the number of components and to prevent an increase in or reduce power consumption of the light source device or the display device.
However, in the above configuration in which the arrangement intervals between the light sources are made wider in the areas corresponding to the end portions of the screen, the following problem may occur. Making the arrangement intervals between the light sources wider increases the difference between the luminance at positions on the screen of the liquid crystal display panel behind which the light sources are located and vicinities thereof and the luminance at positions behind which the light sources are not located (i.e., middle positions between the light sources). Consequently, although the screen luminance is uniform in the center portion of the liquid crystal display panel in which the arrangement intervals between the light sources are narrower, luminance irregularity may occur in the areas corresponding to the end portions in which the arrangement intervals between light sources are wider.